This invention relates broadly to the art of electricity measuring and testing, and more specifically, to circuits for detecting electrical continuity and the presence of various voltages.
The most common type of continuity tester includes a voltage source for producing a current through a circuit to be tested and an indicator for indicating the flow of the current. However, such a continuity tester utilizes too much electrical energy and is too limited in application. With regard to limits to its application, such a continuity tester will only indicate if there is discontinuity in a circuit and will not provide an indication as to the location of the discontinuity. For these reasons, it is an object of this invention to provide a continuity indicator which utilizes very little current but yet not only provides an indication as to continuity, but also provides an indication as to the location of a break in an electrical circuit.
Most prior-art voltage-presence testers provide an indicator, such as a light, which is activated by the passage of an electrical current through two probes attached to opposite terminals of an electrical circuit being tested. When the electrical circuit produces a voltage, electrical current passes through the probes and the indicating device indicates that this voltage is present. However, most prior-art voltage-presence testers are too limited in application in that they will not respond to small spikes of voltage, they will not provide an indication as to the polarity of the voltage, they will not provide an indication of the type of voltage (AC or DC), and they will not provide an indication of the size of the voltage. In addition, many such voltage-presence testers are unduly sensitive and will be damaged by voltages higher than 350 volts. It is an object of this invention to provide a voltage-presence detector which will provide an indication of both very small and very large voltages, will provide an indication of the presence of voltage spikes, will provide an indication of the polarity of a DC voltage, will provide an indication of the type of voltage (AC or DC), and will provide an indication of the size of a voltage. In addition, it is an object of this invention to provide such a voltage-presence detector which is not unduly sensitive and will not be damaged by voltages as high as 1000 volts.
Yet another difficulty with many prior-art voltage presence testers is that they will not store an indication for informing an operator thereof at a later time. This is a disadvantage because when an operator is working alone, he may need to be at a first end of a circuit to send a pulse voltage while his voltage-presence tester is at the other end. In other words, the operator cannot look at the voltage-presence tester at the same time he is sending the pulse voltage in the circuit. This occurs, for example, when someone is testing a doorbell circuit and has the voltage tester at a power box while he is pressing a doorbell button. Thus, it is an object of this invention to provide a voltage-presence tester which will store a voltage-presence indication for a period of time. However, it is also an object of this invention to provide such a voltage tester which is relatively uncomplicated and inexpensive to manufacture.
Yet another difficulty with many prior-art voltage-presence detectors is that two probes thereof must be brought into contact with opposite ends of a circuit in order to get an indication therefrom. That is, one probe has to be attached to a negative terminal of the circuit and the other probe must be attached to a positive terminal of the circuit. Such a shortcoming is quite burdensome because, in some cases it is difficult to gain access to both terminals of a circuit. Also, it is advantageous to be able to determine which of two terminals of a circuit is a "hot" terminal and which is a ground, or common, terminal. For this reason, it is another object of this invention to provide a voltage-presence tester which can work both by having access to two terminals and by having access to only one terminal. Again, it is an object of this invention to provide such a voltage-presence tester which is uncomplicated and relatively inexpensive.